Exaggerate radical-induced DNA damage under magnetic fields is of great concerns to medical biosafety and to biomolecular device based upon DNA electronic conductivity. In this report, the effect of applying an external magnetic field (MF) on DNA-mediated charge transport (CT) was investigated by studying guanine oxidation by a kinetics trap ( 8CP G) via photoirradiation of anthraquinone (AQ) in the presence of an external MF. Positive enhancement in CT efficiencies was observed in both the proximal and distal 8CP G after applying a static MF of 300 mT. MF assisted CT has shown sensitivities to magnetic field strength, duplex structures, and the integrity of base pair stacking. MF effects on spin evolution of charge injection upon AQ irradiation and alignment of base pairs to CT-active conformation during radical propagation were proposed to be the two major factors that MF attributed to facilitate DNA-mediated CT. Herein, our results suggested that the electronic conductivity of duplex DNA can be enhanced by applying an external MF. MF effects on DNA-mediated CT may offer a new avenue for designing DNA-based electronic device, and unraveled MF effects on redox and radical relevant biological processes.

DNA duplexes containing 8-cyclopropyl-2'-deoxyguanosine ((8CP) G) were synthesized to investigate the effect of the C8-modified deoxyguanosine as a kinetic trap for transient hole occupancy on guanines during DNA-mediated hole transport (HT). Thermal denaturation and CD spectra show that DNA duplexes containing (8CP) G are able to form stable B-form duplexes. Photoirradiation of terminal tethered anthraquinone can induce oxidative decomposition of (8CP) G through DNA HT along adenine tracts with lengths of up to 4.8 nm. Shallow and periodic distance dependence was observed in a long adenine tract with intervening guanines. The efficient charge transport indicates that (8CP) G can electronically couple well with a DNA bridge and form HT-active conformational domains to facilitate transient hole delocalization over an adenine tract.

DNA/RNA hybrid duplexes are prevalent in many cellular functions and are an attractive target form for electrochemical biosensing and electric nanodevice. However the electronic conductivities of DNA/RNA hybrid duplex remain relatively unexplored and limited further technological applications. Here cyclopropyl-modified deoxyribose- and ribose-adenosines were developed to explore hole transport (HT) in both DNA duplex and DNA/RNA hybrids by probing the transient hole occupancies on adenine tracts. HT yields through both B-form and A-form double helixes displayed similar shallow distance dependence, although the HT yields of DNA/RNA hybrid duplexes were lower than those of DNA duplexes. The lack of oscillatory periods and direction dependence in HT through both helixes implied efficient hole propagation can be achieved via the hole delocalization and coherent HT over adenine tracts, regardless of the structural variations.

The destabilization effect of 5-hydroxymethylcytosine on CpG repeats can be reversed in heavily methylated duplex.